Slate is a fine-grained, homogeneous rock composed of clay. It is the finest grained foliated metamorphic rock. Many slates will form smooth flat sheets of stone which have long been used for roofing and floor tiles and other purposes. Slate is frequently grey in color. Because of its composition water damage is currently the biggest enemy of Slate’s and Blue Stone’s. The constant humidity could leave a white type of stain in to the surface. Citywide Stone Care can remove these types of stains by using a grinding method and applying special sealants.